To retrospectively assess the predictive value of the CT performed at 24 h, compared with the CT performed at 1 month, in the evaluation of the technical success of microwave (MW) ablation of hepatic lesions. In a single center, 50 patients with HCC underwent percutaneous MW ablation between November 2016 and March 2019. Each patient underwent a contrastenhanced CT exam at 24 h and at 1 month after the procedure. For each patient, was assessed the presence or absence of residual disease, the appearance of a new lesion, complications, and the involvement of the hepatic capsule, both at 24-h and at 1 month. Overall correlation between residual disease, appearance of a new nodule and complications was also assessed. A total of 50 hepatic lesions were treated with US-guided MW ablation. Patients’ mean age was 70.9 years (range 28–87 years). Mean nodule diameter was 17.6 mm (range 7–35 mm). Contingency tables and the χ2 test showed a strong association when looking at capsule involvement (accuracy: 100%), residual disease (accuracy: 90%; p-value 0.003), and the appearance of a new HCC nodule (accuracy: 88%; p-value 0.007); regarding complications, the accuracy was 78% (p-value 0.014). Optimal correlation was reached in 62% of cases, moderate correlation in 26%, minimum correlation in 10% of cases; no cases of zero correlation were recorded. CT at 24 h and 1 month showed comparable efcacy in evaluating residual disease after MW thermal ablation of liver lesions. However, further studies are needed to assess which factors may cause false-negative results at the 24-h CT.
Hepatocellular carcinoma is the ffth most common cancer type, and the second most common cause of cancer-related death globally . The management of HCC is rapidly evolving due to newly introduced novel therapeutic approaches. Imaging-guided ablation gives curative treatment in adequately selected patients or appropriate therapeutic options whether surgical resection or liver transplantation is precluded . Among percutaneous techniques, microwave (MW) ablation is gaining popularity in the ablation of liver tumors with the hope of capitalizing on its potential benefts over RF ablation. These include no need for grounding pads, less susceptibility to the heat sink phenomenon, larger ablation zones, shorter ablation times, and possibly better local tumor control . An early and accurate evaluation of tumor response is essential to assess the efcacy of percutaneous treatments. Current imaging modalities, such as computed tomography (CT) and magnetic resonance (MR) provide reliable and reproducible images to demonstrate tumor burden changes . Traditionally, therapeutic response has been assessed by serial tumor burden measurements according to Response Evaluation Criteria in Solid Tumors (RECIST) or World Health Organization (WHO) criteria [1, 4], which are mainly based on size measurement. However, in liver-directed treatments, simple anatomical changes are not enough informative  and there has been a growing interest to monitor an early response of treatment by measuring tumor viability and/or tumor perfusion. Therefore, it was introduced the concept of tumor enhancement in arterial phase of contrastenhanced imaging studies to characterize only viable target tumors  that lead to the drafting of new guidelines by the European Association for the Study of the Liver (EASL) and American Association for the Study of the Liver Diseases (AASLD). Viable tumor should be defned as uptake of contrast agent in the arterial phase. Consequently, a modifcation of the RECIST criteria (mRECIST criteria) has been adopted . Nevertheless, optimal posttreatment surveillance schedules have been developed for other malignancies, including testicular cancer [7, 8], but not for HCC. In general, guidelines suggest the frst follow-up to be at 1 or 2 months after the procedure to evaluate response but there is still no consensus about an ideal schedule and when the patient should undergo the frst control to assess the complete response [9–11]. The aim of this study is to assess the predictive value of the CT performed at 24 h, compared with the CT performed at 1 month, in the evaluation of the primary technical efcacy (PTE) of microwave (MW) ablation of hepatic lesions.
Materials and methods Population
This was a retrospective study and the approval of our Internal Review Board was waived. Data regarding all patients who underwent percutaneous US-guided MWA for HCC nodules at our institution between November 2016 and July 2019 were collected. Eligible patients were at least 18 years of age with primary non-extrahepatic liver disease only. Patients whose preoperative CT or MRI exams that could not be reviewed were excluded. Patients who could not come to our Institution to perform post-procedural follow-up examinations either at 24 h or at 1 month were also excluded. The resulting population was composed of 50 patients with 1 nodule for person.
For each patient, the following data were registered: age, sex, liver status (normal, hepatitis, or cirrhosis), etiology of liver disease (alcohol, HBV, HCV, non-alcoholic steatohepatitis), and Child Pugh classifcation. Images from the pre-procedural exam, either CT or MRI within 1 month prior to procedure, were reviewed for each patient, and the following data were registered for each HCC nodule: maximum dimension, hepatic segment, and distance from capsule.
Informed consent was obtained from all patients before procedure. An Anesthesiologist assisted the patient during the whole ablation session. Moderate sedation was achieved in each patient through intravenous injection of propofol (0.5–2.0 mg/kg/h), fentanyl (1–2 mcg/kg), and midazolam (0.07–0.08 mg/kg). Vital parameters (heart rate, respiratory rate, blood pressure), together with oxygen saturation and electrocardiographic tracing, were continuously monitored during the procedure. All patients received an antibiotic prophylaxis according to an “ultra-short-term” scheme that consists in preprocedural intravenous administration of cefazolin 1 g, to obtain the drug’s plasmatic concentration peak at the time of ablation and derived cellular necrosis. 10.0 ml of lidocaine 2% solution was injected to obtain local anesthesia in correspondence of the entrance site of the antenna that was positioned under US-guidance (Emprint™ Microwave Ablation System, Covidien, Boulder, CO, USA) in all cases. The ablation system consisted of a microwave generator, capable of producing a power of 100 W at 2450 MHz, connected to a 13.5-gauge straight microwave antenna with a 2.8-cm radiating section by coaxial cable. Continuous perfusion with saline solution at 60 ml/min and at room temperature was provided by the system along the proximal part of the antenna to avoid any thermal damage. Ablation power and time were decided according to data given by the manufacturer and to operator’s preference. The ablation feld was assessed continuously by US during the whole procedure. Ablation power and time were registered for each patient.
Each patient underwent a contrast-enhanced CT exam 24 h and 1 month (range 24–37 days) after the procedure. CT protocol consisted in a standard multiphase contrastenhanced CT (LightSpeed VCT 64; GE Medical Systems, Milwaukee, Wisconsin, USA). The scans were acquired as routine follow-up with the following parameters: 210 mA, 120 kV, 2.5 mm collimation, and pitch of 1.0. For contrast-enhanced CT scans, a body weight adjusted amount of contrast agent (Ultravist 370, Bayer Vital GmbH, Leverkusen, Germany) was injected intravenously with a fow rate of 4 ml/s followed by a 30 ml saline chaser bolus. Scans were started with an 18 s delay for the arterial phase and 45 s delay for the venous phase using the bolus tracking method (threshold, 100 HU). Reports by three radiologists with respectively 4, 10, and 18 years of experience in hepatobiliary imaging were subsequently reviewed.